The default drive letters for user profiles is X:, for public directory P:. This is how to change either or both drive letters for custom needs.
When persistence is enabled, whether Local persistence (enabled by default) or Cloud persistence (shown as CloudSync on Company Settings page--disabled by default), %UserProfile% can be accessed via X:, and C:\Users\Public can be accessed via Y:.
To change these drive letters, connect to server as AdminUser and change system variables accordingly:
If the above System variables do not exist, create them and give them the desired alternate values.